1. Field of the Invention
The present invention relates to a coil and a surface-mounting-type coil component, and more particularly, to a coil defined by flat straight wire which has been edgewise wound and to a surface-mounting-type coil component including the coil.
2. Description of the Related Art
Conventional surface-mounting-type coil components including edgewise wound coils are shown in FIGS. 8 and 9. In the coil component 1 illustrated in FIG. 8, a coil 2 is sandwiched between a pair of E-shaped ferrite core members 3. The coil 2 is formed by concentrically winding a straight wire into a circular configuration (or by subjecting it to edgewise winding). Extending portions 2a and 2b of the coil 2 extend parallel to each other and in the same direction.
In the coil component 5 shown in FIG. 9, a coil 6 is accommodated in a box-shaped ferrite core member 7. The coil 6 is defined by a flat straight wire which has been edgewise wound. A ferrite core member 8 is inserted into a hole 6c in the center portion of the coil 6, and a ferrite core member 9 defining a cover is placed on the core member 8 and the coil 6 to cover them. Extending portions 6a and 6b of the coil 6 are extended parallel to each other and in the same direction.
Ordinarily, the extending portions 2a and 2b of the coil 2 of the coil component 1 are bent along the surfaces of the ferrite core members 3 in order to be used as surface-mounting external electrodes. Similarly, the extending portions 6a and 6b of the coil 6 of the coil component 5 are bent along the surface of the ferrite core member 7 in order to be used as surface-mounting external electrodes. However, the extending portions 2a and 2b of the conventional coil component 1 and the extending portions 6a and 6b of the conventional coil component 5 are arranged at one side of the center of the windings of the coil 2 and at one side of the center of the windings of the coil 6, respectively. Therefore, the coils 2 and 6 in the axial direction are such that the side where the extending portions 2a and 2b and the side where the extending portions 6a and 6b are located are higher than the opposite side where the extending portions 2a and 2b are not located and the opposite side where the extending portions 6a and 6b are not located, respectively. Consequently, when, for example, as shown in FIG. 10, the extending portions 2a and 2b of the coil 2 are bent along the surfaces of the ferrite core members 3, the coil 2 becomes tilted, often causing end portions of the extending portions 2a and 2b to be elevated relative to the surfaces of the ferrite core members 3. This prevents the mounting surface of the conventional coil component 1 from being level, thereby making the component 1 difficult to mount on a printed circuit board.
In addition, when the coil components 1 and 5 are to be mounted on a printed circuit board or other substrate, the surface-mounting external electrodes defined by bending the extending portions 2a and 2b and the surface-mounting external electrodes defined by bending the extending portions 6a and 6b are disposed only on one side of the coil component 1 and the coil component 5, respectively. Thus, the coil components 1 and 5 may get pulled to one side and may be mounted in a tilted state. Further, after being mounted on a printed circuit board, the coil components 1 and 5 are unstable.
The box-shaped ferrite core member 7, the ferrite core member 8, and the ferrite core member 9 of the coil component 5 define a magnetic circuit that is superior to that defined by the pair of E-shaped ferrite core members 3 of the coil component 1. However, even with the magnetic circuit of the coil component 5, the extending portions 6a and 6b of the coil 6 disposed at one side of the center of the windings of the coil 5 locally interrupt the magnetic path, so that magnetic flux lines tend to concentrate at the side where the extending portions 6a and 6b are not disposed (at side A in FIG. 9), which is opposite to the side of the extending portions 6a and 6b. Therefore, magnetic saturation easily occurs, thereby it is difficult to generate inductance with high efficiency. Further, portions P1 at the four corners of the core member 3 of the coil component 1 and portions P2 at the four corners of the core member 7 of the coil component 5 do not function effectively as magnetic circuits, as a result of which space is wasted.
To overcome the problems described above, preferred embodiments of the of the present invention provide a coil and a surface-mounting-type coil component, which enhances mountability and which achieves highly efficient inductance.
According to a preferred embodiment of the present invention, a coil includes an edgewise wound portion and two extending portions extending from two locations of the edgewise wound portion, the two extending portions being arranged to extend opposite to each other so as to be separated by an angle of 180 degrees along a straight line passing through a center of the edgewise wound portion.
This unique structure and arrangement makes it possible to extend the extending portions of the coil using the technique used to wind a straight wire in an edgewise manner. In other words, the extending portions from the respective end of edgewise winding can be easily extended by edgewise bending.
An angle defined by the two locations where the edgewise winding is terminated and an angle formed by the two extending portions may differ. Since the directions in which the extending portions are extended are not restricted, any coil inductance value can be set.
According to another preferred embodiment of the present invention, a surface-mounting-type coil component includes a coil having an edgewise wound portion and two extending portions extending from two locations of the edgewise wound portion, the two extending portions being arranged to extend opposite to each other so as to be separated by an angle of 180 degrees along a straight line passing through a center of the edgewise wound portion, and a core accommodating the coil therein.
The core may preferably be a first core member having a recess for accommodating the coil therein, and a second core member defining a cover and arranged to cover the recess of the first core member.
The first core member is preferably box shaped and may include grooves for accommodating the extending portions of the coil therein. The grooves are preferably located in a side wall defining the recess at 90 degree intervals or at 180 degree intervals.
By virtue of the above-described structures, the two extending portions of the coil are extended in opposite directions so as to be separated by 180 degrees along the straight line that passes through the center of the edgewise wound portion of the coil. Therefore, even when the extending portions are bent along the surface of the core, they are not elevated from the surface of the core. In addition, the surface-mounting external electrodes defined by bending the extending portions are disposed on both sides of the coil component. Therefore, the coil component will not be mounted in a tilted state on a printed circuit board or other substrate, thereby eliminating shaking of the coil component that has been mounted on the printed circuit board. Further, since the extending portions of the coil are not disposed at one side of the center of the winding of the coil, magnetic flux lines are not concentrated at local portions of the core, thereby improving magnetic saturation properties.
When the core includes a box-shaped core member and another core member which defines a cover, a corner of the box-shaped core member may be removed. This allows substantially the entire box-shaped core member to function effectively as a magnetic circuit.
When the box-shaped core member includes grooves for accommodating the extending portions of the coil therein, a corner of the box-shaped core member may be removed.
Other features, elements, advantages and charactestics of the present invention will become apparent from the following detailed description of preferred embodiments with reference to the attached drawings.